Step 1 of 6

Your first variable

So far the program only printed fixed text. Real programs work with data that changes: scores, prices, names. To keep a piece of data around, you store it in a variable.

A variable is a named box in the computer's memory. In C, every box has a type that says what kind of value it can hold, and the type never changes. You create (declare) a variable by writing the type, then the name:

int kills = 25;

int is the type: a whole number (an integer) such as -3, 0 or 25.
kills is the name you'll use to refer to the box.
= 25 puts a starting value in it. This is called initializing the variable.

Printing a variable

printf can't print a number directly inside the quotes, because the text in quotes is fixed. Instead you put a format specifier where the value should appear, and give the value after the string. For an int the specifier is %d (for decimal):

#include <stdio.h>

int main(void) {
    int kills = 25;
    int rounds = 16;
    printf("Kills: %d\n", kills);
    printf("Rounds played: %d\n", rounds);
    return 0;
}

Kills: 25
Rounds played: 16

Naming rules

Names can use letters, digits and underscores, but can't start with a digit, and can't be a C keyword like int or return. Names are case sensitive: score and Score are different variables. Pick names that say what the value means: total_price beats x.

Common mistakes

Using a variable before declaring it: the compiler says 'score' undeclared.
Forgetting to initialize: a variable declared inside a function with no value, like int score;, holds garbage (whatever was in that memory before) until you assign one. Using it before then is a bug the compiler often warns about. Always give variables a starting value.

Your task

Declare an int named score with the value 42.

Challenge 2

Declare two int variables: kills with the value 17 and deaths with the value 9. The program should print Kills: 17 Deaths: 9.

Challenge 3

The printf is already written, but the variables it uses don't exist yet. Declare level (value 7) and xp (value 1250) as int so the program prints Level 7, XP 1250.

Next: Printing values with %d